Abstract: An empirical diffraction based overlay (eDBO) measurement of an overlay error is produced using diffraction signals from a plurality of diffraction based alignment pads from an alignment target. The linearity of the overlay error is tested using the same diffraction signals or a different set of diffraction signals from diffraction based alignment pads. Wavelengths that do not have a linear response to overlay error may be excluded from the measurement error.

Abstract: A dark field diffraction based overlay metrology device illuminates an overlay target that has at least three pads for an axis, the three pads having different programmed offsets. The overlay target may be illuminated using two obliquely incident beams of light from opposite azimuth angles or using normally incident light. Two dark field images of the overlay target are collected using ±1st diffraction orders to produce at least six independent signals. For example, the +1st diffraction order may be collected from one obliquely incident beam of light and the ?1st diffraction order may be collected from the other obliquely incident beam of light. Alternatively, the ±1st diffraction orders may be separately detected from the normally incident light to produce the two dark field images of the overlay target. The six independent signals from the overlay target are used to determine an overlay error for the sample along the axis.

Abstract: A dark field diffraction based overlay metrology device illuminates an overlay target that has at least three pads for an axis, the three pads having different programmed offsets. The overlay target may be illuminated using two obliquely incident beams of light from opposite azimuth angles or using normally incident light. Two dark field images of the overlay target are collected using ±1st diffraction orders to produce at least six independent signals. For example, the +1st diffraction order may be collected from one obliquely incident beam of light and the ?1st diffraction order may be collected from the other obliquely incident beam of light. Alternatively, the ±1st diffraction orders may be separately detected from the normally incident light to produce the two dark field images of the overlay target. The six independent signals from the overlay target are used to determine an overlay error for the sample along the axis.

Abstract: Asymmetry metrology is performed using at least a portion of Mueller matrix elements, including, e.g., the off-diagonal elements of the Mueller matrix. The Mueller matrix may be generated using, e.g., a spectroscopic or angle resolved ellipsometer that may include a rotating compensator. The Mueller matrix is analyzed by fitting at least a portion of the elements to Mueller matrix elements calculated using a rigorous electromagnetic model of the sample or by fitting the off-diagonal elements to a calibrated linear response. The use of the Mueller matrix elements in the asymmetry measurement permits, e.g., overlay analysis using in-chip devices thereby avoiding the need for special off-chip targets.

Abstract: The process of modeling a complex two-dimensional periodic structure is improved by selectively truncating the Fourier expansion used in the calculation of resulting scatter signature from the model. The Fourier expansion is selectively truncated by determining the contribution for each harmonic order in the Fourier transform of the permittivity function and retaining the harmonic orders with a contribution that is above a threshold. The Fourier space may be compressed so that only the selected harmonic orders are used, thereby reducing the required memory and calculation times. The compressed Fourier space may be used in a real-time analysis of a sample or to generate a library that is used in the analysis of a sample.

Abstract: An empirical diffraction based overlay (eDBO) measurement of an overlay error is produced using diffraction signals from a plurality of diffraction based alignment pads from an alignment target. The linearity of the overlay error is tested using the same diffraction signals or a different set of diffraction signals from diffraction based alignment pads. Wavelengths that do not have a linear response to overlay error may be excluded from the measurement error.

Abstract: Asymmetry metrology is performed using at least a portion of Mueller matrix elements, including, e.g., the off-diagonal elements of the Mueller matrix. The Mueller matrix may be generated using, e.g., a spectroscopic or angle resolved ellipsometer that may include a rotating compensator. The Mueller matrix is analyzed by fitting at least a portion of the elements to Mueller matrix elements calculated using a rigorous electromagnetic model of the sample or by fitting the off-diagonal elements to a calibrated linear response. The use of the Mueller matrix elements in the asymmetry measurement permits, e.g., overlay analysis using in-chip devices thereby avoiding the need for special off-chip targets.

Abstract: The process of modeling a complex two-dimensional periodic structure is improved by selectively truncating the Fourier expansion used in the calculation of resulting scatter signature from the model. The Fourier expansion is selectively truncated by determining the contribution for each harmonic order in the Fourier transform of the permittivity function and retaining the harmonic orders with a contribution that is above a threshold. The Fourier space may be compressed so that only the selected harmonic orders are used, thereby reducing the required memory and calculation times. The compressed Fourier space may be used in a real-time analysis of a sample or to generate a library that is used in the analysis of a sample.

Abstract: An overlay error is determined using a diffraction based overlay target by generating a number of narrow band illumination beams that illuminate the overlay target. Each beam has a different range of wavelengths. Images of the overlay target are produced for each different range of wavelengths. An intensity value is then determined for each range of wavelengths. In an embodiment in which the overlay target includes a plurality of measurement pads, which may be illuminated and imaged simultaneously, an intensity value for each measurement pad in each image is determined. The intensity value may be determined statistically, such as by summing, finding the mean or median of the intensity values of pixels in the image. Spectra is then constructed using the determined intensity value, e.g., for each measurement pad. Using the constructed spectra, the overlay error may then be determined.

Abstract: A diffraction based overlay metrology system produces the overlay error independent of effects caused by local process variations. Generally, overlay patterns include process variations that provide spectral contributions, along with the overlay shift, to the measured overlay error. The contributions from process variations are removed from the determined overlay error. In one embodiment, the local process variations are removed by measuring the overlay pattern before and after the top diffraction gratings are formed. A plurality of differential spectra from the measurement locations of the completed overlay pattern can then be used with a plurality of ratios of differential spectra from measurement locations of the incomplete overlay pattern can then be used to determine the overlay error by either direct calculation or by fitting techniques. In another embodiment, the local process variations are removed with no premeasurement but with careful construction of the overlay patterns.

Abstract: An alignment target includes periodic patterns on two elements. The periodic patterns are aligned when the two elements are properly aligned. By measuring the two periodic patterns with an incident beam having a single polarization state and detecting the intensity of the resulting polarized light, it can be determined if the two elements are aligned. The same polarization state may be detected as is incident or different polarization states may be used. A reference measurement location may be used that includes a third periodic pattern on the first element and a fourth periodic pattern on the second element, which have a designed in offset, i.e., an offset when there is an offset of a known magnitude when the first and second element are properly aligned. The reference measurement location is similarly measured with a single polarization state.